For centuries, positive properties of yeasts were utilised in the production of alcohol as well as in bread making. Yeasts are unicellular fungi that multiply in the presence of heat and moisture and metabolize carbohydrates. The most commonly used strain is Saccharomyces cerevisiae, also known as brewer’s or baker’s yeast.
In practice, however, a distinction must be made between the use of spent brewer’s yeast and live yeast. Both are yeasts of the strain Saccharomyces cerevisiae. However, spent brewer’s yeast is a by-product of the brewing process and is fed as staple feed, fresh or dried, because of its nutritional value. These inactivated yeasts possess valuable protein, are rich in B vitamins and other co-factors. Live yeasts, on the other hand, are metabolically active yeasts that are bred specifically for animal nutrition. They are considered feed additives.
In general, the positive effects of live yeast are based on its probiotic action. As a digestive aid, it displaces unwanted microorganisms and stabilises a natural balance in the intestine or rumen. The use of live yeast in cattle feeding has been shown to have positive effects on rumen metabolism (Figure 1). These effects lead to healthier and more productive animals in the long term.
Figure 1: Positive effects of live yeast on rumen metabolism
In general, live yeasts in dairy cattle feed provide optimal conditions for the rumen microbes. The activity and growth of desired bacteria is positively influenced by the utilisation of residual oxygen as well as by the availability of micronutrients.
- These bacteria include the lactate-utilising bacteria. These keep the concentration of lactate in the rumen as low as possible and thus stabilise the pH value of the rumen. As a result, the risk of rumen acidosis decreases.
- The cellulolytic bacteria are also promoted. These are responsible for an effective crude fibre degradation. This results in the following: increased utilisation of crude fibre leads to an improved feed conversion due to a growth in volatile fatty acids, while simultaneously stimulating feed intake.
- Reproduction of both groups of bacteria increases ammonia utilisation and promotes a bacterial protein synthesis. It can therefore be assumed that more microbial protein reaches the small intestine and is available to the animal for utilisation.
A newborn calf initially has a non-functional rumen. The absorbed fluid reaches the abomasum as a result of the pharyngeal reflex. As soon as the young animal takes in solids in the form of roughage, calf TMR or calf muesli, the use of live yeast is recommended.
Absorbed solid feed reaches the rumen and stimulates rumen activity. As a rule, the same effects occur in the adult cow. Live yeasts promote raw fibre utilisation and stimulate feed intake. This enables the young animal to use larger quantities of solid feed at an early age. This has a positive effect on the daily weight gain of the calves. At the same time, supporting roughage digestion reduces the stress of weaning, so that the “developmental gap” that occurs after weaning is cushioned.
The results of recent studies indicate that acidosis in calves is not an exception but is often the rule. If the rumen is not yet fully developed, calves can develop subclinical rumen acidosis at an early age if they switch to solid feed early on. Live yeast can reduce the risk. Both as a precautionary measure and in acute cases, live yeasts stabilise the rumen environment through their lactate-reducing effect.
In addition, calves’ health status is reported to improve. The use of live yeast led to firmer excrement and reduced the number of days with diarrhoea. This effect is possibly related to the property of yeast cell walls to bind toxins or even enterobacteria such as E.Coli.
All in all, the use of live yeast promotes healthy and rapid growth of young calves that grow into vital, high-performing dairy cows and keeps rearing costs low.
Live yeasts do not settle permanently in the animal’s digestive tract. With a single dose, the yeast cells live for about 30 hours in the rumen without multiplying. It is therefore important to supply live yeast to the animal daily with the feed. As a rule, live yeast cultures are already mixed into mineral, concentrated, supplementary or special feed and do not have to be specifically added to the ration.
It should also be taken into account that the rumen microbes need 2-3 weeks to adapt. This corresponds to the normal adaptation phase of a ration change. After this time, the positive effects of live yeast are usually visible.
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